Downing Street has been told it should disclose some of the dates on which Tony Blair met Rupert Murdoch, the head of News Corp, or provide a better explanation for refusing to do so.

Following a 17-month campaign by Lord Avebury, the Liberal Democrat peer, the information commissioner has ordered the Cabinet Office to reveal the dates under the Freedom of Information Act or explain its failure to do so.

Lord Avebury is not seeking details of the meetings, but their timing. He says the public should be able to make up its own mind on the influence on government of Mr Murdoch and that of Richard Desmond, the Daily Express proprietor.

The Cabinet Office has twice rejected the request for the information, saying that "disclosure would undermine the prime minister's ability to hold free and frank discussions in the future".

The information commissioner, in his ruling, argues that in this instance there is a stronger public interest in understanding more about the workings of government. He says there may be exemptions to this ruling if disclosure is inimical to the public interest.

Mr Blair is due to deliver a lecture at a conference of Mr Murdoch's executives at the end of the month in California.